1. Field of the Invention
The present invention relates generally to audio systems, and in particular to audio systems for motor vehicles.
2. Description of Related Art
A great number and variety of audio systems for sound and musical playback are available. A basic audio system may be as simple as an AM/FM radio and a loudspeaker. More sophisticated systems often include the ability to play many different types of media, including cassette tapes, compact disks (CDs), and, in some cases, digital versatile disks (DVDs).
Some audio systems include sound enhancement features. While many basic audio systems are capable of two-channel (stereo) playback, other more sophisticated audio systems are capable of reproducing more channels of sound (multi-channel sound). If an audio source does not provide enough data or channels for more than two channels of sound, some audio systems may use algorithms to simulate additional channels of sound to create, for example, a simulated 5.1 channel surround sound playback from a two-channel audio source. Examples of these sound enhancement algorithms include Dolby Pro-Logic II™, DTS Circle Surround™, and Bose Centerpoint™.
A CD stores two channels of audio at known bit rate which is an industry standard, 44.1 kHz. Since the CD is currently the overwhelming preference in media formats used today, it can be assumed that all enhanced playback algorithms use this as a reference to tune their performance. Because audio information stored on a CD using a traditional CD audio format is generally of relatively high quality, the audio played from a CD will sound good when an enhanced playback algorithm, such as a simulated surround sound playback algorithm, is used.
More recently, however, different formats and media are used to store digital audio information. Some audio systems allow hard disk drives with stored digital audio to be directly connected to the system. Other audio systems are capable of reading an optical disk, such as a CD-ROM or DVD with digital audio information stored in a digital audio file format. In some cases, a file format different than the one used for a traditional CD is used.
When audio is stored digitally in a format other than the traditional CD audio format, digital audio information can be stored in many different storage formats and quality levels. Moreover, the quality of the recording may be deliberately reduced in order to store more audio in the same amount of space. This process of reducing the size of a digital audio file is referred to as compression.
Compression algorithms are optimized by eliminating information in the audio signal that is not readily perceived by human hearing, thus giving the best sound quality while reducing the file size. It is known that there is a trade off between audio performance and file size. Since these enhancement algorithms also use the same information in the audio stream to simulate surround sound, the higher the compression, the less effective the simulation. Because of this, some compressed digital audio files may not sound good when played back using an enhanced mode. Even if a digital audio file sounds good in a non-enhanced playback mode (e.g., two-channel stereo), the sound quality may deteriorate if a simulated surround sound or other enhanced playback algorithm is used.
Motor vehicles typically include at least a basic audio system, although more sophisticated audio systems with enhanced playback algorithms are also available. As audio systems need to process and playback various different types of digital audio files, and as hard disk drives and hard disk drive docking devices become more common in motor vehicle audio systems, audio systems need to be increasingly versatile. These systems must be able to receive, process and properly playback a variety of different types of digital audio files. Current audio systems lack these, as well as other abilities.